1. Field of the Invention
The present invention relates to a radar apparatus used for example in an automotive vehicle collision prevention systems.
2. Background Art
As an essential element of, for example, an automotive vehicle collision prevention system, vehicle radar apparatuses are under development that detect the distance to objects such as the vehicle in front or an approaching vehicle. Recently, scanning-type radar apparatuses are also being developed that can detect not only the distance to the object, but also the direction of the object seen from the source vehicle.
Among scanning-type radar apparatuses, the electronic scanning type is structured so that the antenna apparatuses, which radiate a light wave, electro-magnetic, or ultra-sound wave beam, and receive the reflected waves, are arranged in plurality with slightly offset directionalities to each other, and by carrying out transmission and reception of the beam from each antenna in the order of their arrangement, detect from which antenna apparatus, that is, from which direction, the reflected wave was generated. In this type of electronic scanning-type radar apparatus, the various transmitting and receiving directions of the plurality of discretely arranged electric waves are called signal transmission and reception channels, or simply channels, and the apparatus as a whole is called a multi-channel-type radar apparatus.
In contrast to the transceiving mode in which the reflected waves of a beam transmitted by a given channel are received by that same channel, some multi-channel type radar apparatuses are structured so that the directional resolution is improved with a limited number of transceiving antennas by adding a transceiving mode in which the reflected wave of the beam transmitted by one channel is received by an adjacent channel. The applicants of the present application disclose the improvement of the directional resolution that accompanies parallel used of this transceiving mode in U.S. Pat. No. RE 36,095 and U.S. Pat. No. 5,448,244.
In the transceiving mode extending over adjacent channels, adding virtual transceiving antennas between the transceiver antennas of the adjacent channels has the same effect, and the directional resolution is improved. The transceiving channel added along with the addition of these virtual transceiving antennas are called bistatic channels. In addition, in order to distinguish this type of bistatic channel, a transceiving channel that receives by one channel the reflected beam of a beam transmitted from that same channel is called a monostatic channel. Moreover, there are cases when one transceiving channel is considered to include bistatic channels and monostatic channels, cases of using one antenna for both transmission and reception, and cases of using individual antennas used separately for transmitting and receiving.
The total number of channels is increased and the position resolution is improved with a limited number of antennas by using together the above-described monostatic channels and bistatic channels. However, because the directionality of the virtual antennas of these bistatic channels is given as the sum of the directionalities of antennas which include respective adjacent channels and mutually offset dispositions, compared to the directionality of the antenna of the monostatic channels, the side lobes become large. In addition, due to the existence of these side lobes, there is the concern that the detection precision will deteriorate.
In consideration of this point, from the viewpoint of the improvement of detection precision, the conventional method of continuous use of monostatic channels and bistatic channels together is not necessarily always optimal. Therefore, an object of the present invention is to realize maximally precise detection in a multi-channel radar apparatus having a system that uses monostatic channels and bistatic channels together.
Another object of the present invention is to optimize the total number of channels used in a general multi-channel radar apparatus. This is because there are also the problems that when the number of used channels is large, the processing for the detection of the reflected wave and the calculation of the center of gravity, etc., consumes time, and that the tracking capacity during a rapid change in the scanning state on the road, etc., may deteriorate.
The multi-channel radar apparatus according to one aspect of the present invention for solving the above-described problems of the conventional technology is structured so as to detect direction using only a monostatic channel reception signal when the reception level is larger than a predetermined threshold value, and using a monostatic channel reception signal and a bistatic channel reception signal when the reception level is equal to or less than this threshold value.
The multi-channel radar apparatus according to another aspect of the present invention for solving the above-described problems of the conventional technology is structured so as to detect direction using a reduced number of said channels for detecting an object as a level of received signals increases.
The multi-channel radar apparatus according to the present invention for solving the above-described problems of the conventional technology is structured so as to reduce the time for detecting the reflected signal and processing the received signals and improving the tracking capacity while maintaining or improving the precision by reducing the number of used channels according to the size of the level of the received signal.